Implantable vascular grafts are used in medical applications for the treatment of diseased or damaged blood vessels, such as arteries and veins. Such treatment may be necessitated by conditions in the arteries and veins, such as a stenosis, thrombosis, occlusion or aneurysm. A vascular graft may be used to repair, replace, or otherwise correct a diseased or damaged blood vessel.
A vascular graft may be a tubular prosthesis for replacement or repair of a damaged or diseased blood vessel. To maximize the effectiveness of such a prosthesis, it should be designed with characteristics which closely resemble that of the natural body lumen which is being repaired or replaced by the prosthesis.
An implantable vascular graft may be a multi-layered composite. The multi-layered composite may include a first layer formed of a textile material and a second layer formed of expanded polytetrafluoroethylene (ePTFE) having a porous microstructure defined by nodes interconnected by fibrils. An elastomeric bonding agent is applied to either the first or the second layer and disposed within the pores of the microstructure for securing the first layer to the second layer. An implantable vascular graft may therefore include an ePTFE-lined textile graft, an ePTFE graft, covered with a textile covering, or a vascular patch including a textile surface and an opposed ePTFE surface. Such a vascular graft may include additional ePTFE and/or textile layers.
The ePTFE may be formed from extruded tubes. PTFE is particularly suitable as an implantable prosthesis as it has good biocompatibility and low thrombogenicity. ePTFE has a microporous structure which allows natural tissue ingrowth and cell endothelization once implanted in the vascular system. This contributes to long term healing and patency of the graft.
A hybrid vascular graft may be used in the vascular system, urogenital tract and bile duct, as well as in a variety of other applications in the body. A hybrid vascular graft may be reinforced to open and support various lumens in the body. Such a hybrid vascular graft may be used for the treatment of stenosis, strictures and aneurysms in blood vessels, such as arteries and veins. Such treatments include implanting the vascular graft within the blood vessel to open and/or reinforce collapsing or partially occluded sections of the vessel.
A hybrid vascular graft may be reinforced by providing a stent between the outer layer formed of textile and the inner tubular layer formed of non-textile, such as ePTFE material. Such a composite structure is disclosed in FIGS. 18 and 20 and the related text of U.S. Patent Application Publication No. U.S. 2003/0204241. The entire disclosure of U.S. Patent Application Publication No. U.S. 2003/0204241 is hereby incorporated by reference herein. A stent constituted by a helical coil is disclosed in FIG. 8 and the related text of U.S. Patent Application Publication No. US 2003/0204241.
The reinforcement provided by a stent, such as a helical coil, between the outer and inner tubes of a hybrid vascular graft is generally uniform in the longitudinal and radial directions along the vascular graft. Such uniformity is advantageous for some uses of the vascular graft. However, for other uses, it is preferable for the reinforcement to vary in the longitudinal and radial directions along the vascular graft.
A stent, such as a helical coil, located between the outer and inner tubes of a hybrid vascular graft is typically bonded to the tubes. Accordingly, assembly of such a vascular graft may include handling the stent in addition to the outer and inner tubes, positioning the stent relative to the tubes before the bonding together of the tubes, and securing the stent to the tubes. This may add complexity to and require additional effort for the assembly of the vascular graft. Additionally, the material of the stent must normally be compatible with materials of outer and inner layers, and possibly with the body of the patient. This may limit the type of material which is suitable for the stent. Additionally, it may be desirable to bond the outer and inner tubes together before attachment of the stent thereto.